Yes, Virginia, reindeer can have red noses (even if they don't glow)

Reindeer's hairy snouts were, on average, 25 percent more densely packed with tiny blood vessels, or capillaries, than those of their human counterparts.

More than 70 years after the publication of Robert May’s Christmas tale, “Rudolph the Red-Nosed Reindeer,” scientists have finally gotten around to investigating exactly why the noses of reindeer (or caribou, as we prefer to call them in North America) sometimes take on a distinctively ruby hue.

A definitive study on the topic was published this week in the Christmas issue of the medical journal BMJ, which each year features a few holiday-oriented scientific studies (with tongue planted firmly in cheek).

For the study, a group of Dutch and Norwegian researchers used a hand-held video microscope to examine and compare the noses of two reindeer and five human volunteers. They found that the reindeer's hairy snouts were, on average, 25 percent more densely packed with tiny blood vessels, or capillaries, than those of their human counterparts.

The scientists point out that extra-dense blood vessels are probably quite helpful for regulating body temperature in the extreme cold of the Arctic, the reindeers’ home turf. And indeed, when infrared thermographic images were taken of the study’s reindeer as they exercised on a treadmill (!), it was discovered that the two hottest areas on the animals’ bodies were their hind legs and their nose.

This finding suggests that the thickness of the capillaries on the animals’ snouts helps keep the animals from overheating. Heat is delivered through the capillaries to the skin, where it is then released out of the body. The more capillaries, the more efficiently the process works — and the redder the nose. (There was no finding, however, that the reindeer's noses ever glow.)

“We were able to solve an age old mystery,” the authors conclude. “Rudolph’s nose is red because it is richly supplied with red blood cells, comprises a highly dense microcirculation, and is anatomically and physiologically adapted for reindeer to carry out their flying duties for Santa Claus.”

“We thank Santa Claus for his enthusiastic support,” they add in the study’s acknowledgements. “He was as keen as us to unravel the mystery of his friend’s nose.”